THE PANEL GAME

Structural Insulated Panels, commonly known as SIPs, have been used in America for over 50 years and have gained a modest foothold in the U.K over the past 20 years or so. The panels are quick to erect and give unrivalled insulation. Many of the first UK SIPS buildings were built purely for their insulation benefits to build cold stores, structures for indoor ice climbing walls, and snow domes all of which are designed to keep heat out but of course insulation works both ways.

Modern SIPs are made from high density facing materials such as Oriented Strand Board (OSB) or Cement Bonded Particleboard (CPB). The core can be either polyurethane foam (PUR) or lower grade insulation such as Expanded Polystyrene (EPS.) One of the early UK pioneers of SIPS was Tony Palmer MD of SIPTEC. Palmer worked on developments such as Stevenage New Town and Milton Keynes, and witnessed the first rot out failures of timber frame construction. With the onset of the energy crisis and price increases in the 70’s he recognised the urgent need to apply additional insulation to standard building cavity wall construction. During this period he took several products through Agrément certification (the forerunner to BBA) and predicted the failure of the UF Foam cavity wall insulation systems that lead to their removal from the market.

To this date he believes there was nothing basically wrong with the UF Foam product, his opinion is that the problems occurred through lack of control and inadequate supervision over installation and he is convinced that the same problems will occur with SIPs building systems unless a responsible authority polices and controls the design and on site build process, in a similar way to the TRADA Timber frame Inspection scheme. Palmer is currently assisting TRADA in developing such a programme with the ultimate aim of CE certification. He is firmly convinced that experiments he has made utilising continuous wet lamination methods will emerge as 'the ultimate' 'SIP Production Technology'. In the early days it was very difficult to convince people to trial Palmer's SIP products here in the UK but the company successfully exported its Elite Composite panels into Europe, mainly France and Greece. Tony Palmer recalls that, on one occasion, half the staff of the BRE looked on in amazement at compressive tests taking place in their heavy structures laboratory; they could not believe the strength of panels comprising extruded polystyrene cores with 9mm plywood faces.

Development in the UK went forward using OSB material from the newly established plants in the UK and Ireland and EPS manufactured in the UK. It almost immediately became apparent that potentially very serious density variation was occurring with the block EPS that was being bought in, whilst the specification claimed 15kgs per cubic meter, on occasions it was found to be as low as 6kgs. If such a low density core was used in a lamination with a structural point loading there was the chance of structural failure. During a very hot summer in Greece, Tony Palmer noticed that samples of EPS material left in his car had softened and bent in the high temperatures, this gave him cause for concern because in the USA, where EPS was prevalent, they call for only 15 minute fire resistance in housing structures, whereas UK building regulations required 30 minutes.

Elite Composites, therefore decided to develop polyurethane cored structural insulated panels as this material was know to be much more stable in high temperature and it give a far superior insulation value. This development led to the product produced today by SIPTEC licensed plants. The PUR foam is pressure injected into the panel and must be dense and well adhered. If you can rub the foam core out with a finger then the panel is sub standard and should not be used as structural.